Mature offshore oil
& gas fields with declining production such as the North Sea are facing
increasing decommissioning costs. It is estimated that over the next decade, about £20 billion will be spent on decommissioning.
“OEUK’s Decommissioning Insight 2023 report offers a
unique overview of the challenges and market opportunities in the sector which
involve some of the biggest and most complex engineering projects ever faced in
the North Sea.”
“The report highlights that shutting down obsolete North
Sea energy installations is a business opportunity worth more than £20 billion
over the next decade, according to calculations by Offshore Energies UK (OEUK).
The report also gives a detailed overview of requirements for decommissioning
and recycling hundreds of oil and gas platforms in UK, Norwegian, Danish and
Dutch waters.”
According to the World Economic Forum:
“The North Sea has more than 1,500 platforms and
installations with an average age of 25 years.”
“Another 1,500 oil and gas platforms are more than 30
years old in the Gulf of Mexico.”
“And in the Asia–Pacific region, more than 2,500
platforms will need to be decommissioned in the next decade.”
While that is a
lot to spend, the costs of decommissioning have been dropping and are predicted
to drop a further 10% by 2028. However, that remains to be seen as costs have
crept up over the past year. In the North Sea decommissioning of wells is set
to account for 51% of expenditure of the next decade. By 2030, 180 of the 280
fields in the North Sea are expected to be no longer in production. 2100 wells
are expected to be decommissioned in the next decade. Thus, for the region,
decommissioning projects are going to be very common in the years ahead. It is important that different companies work together in decommissioning to save money, time, and emissions, and to find synergies. Several
graphics from the North Sea report are shown below.
Structure and Materials Recycling: Mainly Above Sea,
or ‘Topside’ Infrastructure
The above sea, or ‘topside’ parts of platforms are typically dismantled and dragged onshore to be repurposed or recycled. The peak of onshoring these parts and materials is expected to occur in the North Sea UK in 2027, with 250,000 tons of material expected to come ashore. Parts like valves can be reused in other oil & gas fields. Concrete mattress removals for reuse elsewhere are becoming more common in decommissioning. In the North Sea, there are 40,000 concrete mattresses to be recovered by 2030, They can be reused in the construction and agricultural industries. As I recount later many platform substructures as well as sunken topsides could be used as reefs to enhance biodiversity and for use by divers. The graphic below shows three common methods of platform 'reefing.'
Repurposing: Keeping Platforms for Offshore Wind,
Hydrogen, CCS, Floating LNG, etc.
Many offshore platforms
are repurposed for offshore wind infrastructure, floating LNG terminals, or
infrastructure for hydrogen and CCS. A 2019 UKCS report explored possible scenarios
of repurposing platforms for use in these ‘green energy hubs.’ Another
potential innovation is electrifying the oilfields with nearby wind farms. Norway
has led offshore electrification in recent years.
Offshore oil & gas decommissioning is also informing offshore wind decommissioning. There are areas in the North Sea where offshore wind decommissioning will grow in the years ahead.
As shown
below, gas-to-wire electrification can be a very useful option to utilize
stranded gas, decrease GHG emissions, and save costs.
Onsite Separation Technologies for Waste Fluids
Decommissioning
involves cleaning up a number of waste streams including oil sludge and
oil-contaminated water. Typically, these contaminated fluids are shipped off to
be treated elsewhere in a process known as “skipping and shipping.” However,
treating these waste fluids onsite is now becoming an option. The deployment of
separation technologies can save money and reduce emissions compared to other
treatment options. One of these technologies utilizes centrifuging to separate particles
by density. This has long been used in the oil & gas industry to remove
solids from drilling mud. The unit shown below is a decanter centrifuge.
A second separation
device commonly used in decommissioning is a disc stack separator. Combined
with a decanter centrifuge the two devices together can recover saleable oil
from waste oil, remove solids, separate radioactive fluids, and separate water
that can also be treated onsite in an effluent treatment plant. Wastewater with
less than 30ppm of oil can be discharged into the sea and onsite treatment can
get much of the water to that standard. Treating onsite saves quite a bit in
transportation costs and subsequent carbon emissions. The article in World Oil
mentions a decommissioning project where 8000 cubic meters of waste fluids and
solids were treated onsite and 79% of the treated wastewater was below the 30-ppm
limit. Onsite treatment can also operate during normal operations so that these
systems can run more or less continuously, saving time during decommissioning. Treating
onsite is also safer since it eliminates all transportation risks.
Repurposing Offshore Oil and Gas Infrastructure:
Rigs-to-Reefs
Repurposing
oil and gas infrastructure can take many forms. Offshore drilling and
production platforms can be utilized for offshore wind or floating LNG functions
or support. It has long been known that in certain places and at certain water
depths and properties, the underwater parts of offshore platforms can support
aquatic communities and even develop thriving reefs increasing ocean biomass.
There are about 6000 offshore platforms globally and on average they provide
about 2 to 3 acres of habitat {I am unsure of that number since other reports say
that there are about 12,000 platforms globally}. That adds up to 15,000 acres
{or 30,000}. A 2014 study published in the Proceedings of the National Academy
of Sciences found that offshore platforms off the coast of California were “among
the most productive marine fish habitats globally” and may be among the
most productive ecosystems in the world. Thus, decommissioning of these
platforms now can involve leaving much of the underwater components intact so
that the artificial reefs keep providing ecosystem services. This can save
companies millions in decommissioning costs. It is not applicable to all
platforms and things to be considered include location, water depth, stability,
structural characteristics, and age. Complete removal is still the main
practice in the US but that is changing. In the past 30 years, about 500
platforms in the Gulf of Mexico have been retained as artificial reefs. This is
an example of a circular economy. This has potential use for offshore wind and
tidal platforms as well.[1] [2]
References:
Oil's
well that ends well: Recovering value, managing costs and reducing emissions
during decommissioning. Rory MacKenzie. World Oil. October 2024. Decommissioning—Mackenzie
(OSSO)
Decommissioning
Insight 2023. The decommissioning outlook for the UK’s offshore energy industry.
The UK Offshore Energies Association Limited (trading as Off shore Energies UK).
Decommissioning-Insight-2023-OEUK-sac2nq.pdf
What
to do with ageing oil and gas platforms – and why it matters. World Economic
Forum. April 2, 2024. Ageing
oil and gas platforms – here’s what to do with them | World Economic Forum
UKCS
Energy Integration: Interim findings. Oil & Gas Authority. December 2019. ukcs_energy_integration-_interim_findings.pdf
[1]
Oil platforms among most productive fish habitats. Jeremy T. Claisse, Daniel J.
Pondella, Milton Love, Laurel A. Zahn, Chelsea M. Williams, Jonathan P.
Williams, Ann S. Bull Proceedings of the National Academy of Sciences Oct 2014,
11 (43) 15462-1546. Oil
platforms off California are among the most productive marine fish habitats
globally | PNAS
[2]
Hazelwood, Emily and Sparks, Amber. Rigs as reefs: An opportunity for creative,
sustainable resource management. World Oil. August 2021. Vol 242 No. 8. Rigs
as reefs: An opportunity for creative, sustainable resource management
(worldoil.com)
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